Separator for zinc secondary battery

ABSTRACT

The present disclosure provides a separator for a zinc secondary battery that can inhibit short circuiting in a zinc secondary battery. The separator for a zinc secondary battery of the disclosure has a porous substrate layer and a titanium oxide-containing porous layer laminated onto the porous substrate layer, wherein the titanium oxide-containing porous layer comprises a titanium oxide represented by TixOy, where 0&lt;x, 0&lt;y, and y&lt;2x. The titanium oxide may be TiO, Ti2O, Ti2O3, Ti3O, Ti3O5, Ti4O5, Ti4O7, Ti5O9, Ti6O, Ti6O11, T17O13, T18O15 or T19O17.

FIELD

The present disclosure relates to a separator for a zinc secondarybattery.

BACKGROUND

In a zinc secondary battery such as a nickel zinc secondary battery orair zinc secondary battery, it is known that repeated charge-dischargecauses the zinc in the negative electrode to form dendrites. Growth ofthe dendrites beyond the separator and reaching the positive electrodebody can result in short circuiting of the zinc secondary battery. Aneed therefore exists for technology to inhibit short circuiting causedby growth of dendrites in zinc secondary batteries.

In regard to this problem, PTL 1 discloses a porous film situatedbetween the positive electrode body and negative electrode body of azinc battery, the porous film comprising a metal oxide havingisoelectric points 5 to 11. The same publication mentions titaniumdioxide, aluminum oxide and beryllium oxide as examples of metal oxidesin the porous film.

CITATION LIST Patent Literature

-   [PTL 1] Japanese Unexamined Patent Publication No. 2019-216057

SUMMARY Technical Problem

In a zinc secondary battery, it is desirable to inhibit short circuitingcaused by zinc dendrites grown from the negative electrode body reachingto the positive electrode body.

PTL 1 teaches that short circuiting can be inhibited by the porous filmwhich it discloses. Further inhibition of short circuiting in zincsecondary batteries is desired, however.

It is an object of the present disclosure to provide a separator for azinc secondary battery that can inhibit short circuiting in a zincsecondary battery.

Solution to Problem

The present inventors have found that the aforementioned object can beachieved by the following means:

<Aspect 1>

A separator for a zinc secondary battery, having a porous substratelayer and a titanium oxide-containing porous layer laminated onto theporous substrate layer, wherein the titanium oxide-containing porouslayer comprises a titanium oxide represented by Ti_(x)O_(y), where 0<x,0<y, and y<2x.

<Aspect 2>

The separator for a zinc secondary battery according to aspect 1,wherein the titanium oxide is TiO, Ti₂O, Ti₂O₃, Ti₃O, Ti₃O₅, Ti₄O₅,Ti₄O₇, Ti₅O₉, Ti₆O, Ti₆O₁₁, Ti₇O₁₃, Ti₈O₁₅ or Ti₉O₁₇.

<Aspect 3>

The separator for a zinc secondary battery according to aspect 1 or 2,wherein the porous substrate layer, the titanium oxide-containing porouslayer and the porous substrate layer are laminated in that order.

<Aspect 4>

The separator for a zinc secondary battery according to aspect 3,wherein a nonwoven fabric layer, the porous substrate layer, thetitanium oxide-containing porous layer and the porous substrate layerare laminated in that order.

<Aspect 5>

The separator for a zinc secondary battery according to any one ofaspects 1 to 4, wherein the porous substrate layer is a resin porouslayer.

<Aspect 6>

The separator for a zinc secondary battery according to aspect 5,wherein the resin porous layer is a polyolefin-based porous layer, apolyamide-based porous layer or a nylon-based porous layer.

<Aspect 7>

A zinc secondary battery having a separator for a zinc secondary batteryaccording to any one of aspects 1 to 6.

<Aspect 8>

The zinc secondary battery according to aspect 7, which has a negativeelectrode body, the separator for a zinc secondary battery and apositive electrode body in that order, and the negative electrode body,the separator for a zinc secondary battery and the positive electrodebody are impregnated with an electrolyte solution.

<Aspect 9>

The zinc secondary battery according to aspect 8, wherein theelectrolyte solution is an aqueous solution.

<Aspect 10>

The zinc secondary battery according to aspect 8 or 9, wherein theelectrolyte solution is an alkali electrolyte solution.

<Aspect 11>

The zinc secondary battery according to any one of aspects 8 to 10,wherein zinc oxide is dissolved in the electrolyte solution.

Advantageous Effects of Invention

According to the present disclosure it is possible to provide aseparator for a zinc secondary battery that can inhibit short circuitingin a zinc secondary battery.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing a separator for a zinc secondarybattery 10 according to a first embodiment of the disclosure.

FIG. 2 is a schematic diagram showing a separator for a zinc secondarybattery 10′ according to a second embodiment of the disclosure.

FIG. 3 is a schematic diagram showing a separator for a zinc secondarybattery 10″ according to a third embodiment of the disclosure.

FIG. 4 is a schematic diagram showing a zinc secondary battery 100according to a first embodiment of the disclosure.

FIG. 5 is a graph showing evaluation results for cycle stability inComparative Examples 2 and 3 and Examples 1 and 2.

DESCRIPTION OF EMBODIMENTS

Embodiments of the disclosure will now be described in detail. Thedisclosure is not limited to the embodiments described below, however,and various modifications may be implemented which do not depart fromthe gist thereof

<Separator for Zinc Secondary Battery>

The separator for a zinc secondary battery according to the disclosurehas a porous substrate layer, and a titanium oxide-containing porouslayer laminated on the porous substrate layer. The titaniumoxide-containing porous layer comprises a titanium oxide represented byTi_(x)O_(y), wherein 0<x, 0<y, and y<2x.

The zinc secondary battery to which the separator for a zinc secondarybattery of the disclosure can be applied may be a zinc secondary batteryhaving a negative electrode body, a separator and a positive electrodebody housed in that order in a battery case, and having the battery casefilled with an electrolyte solution. The zinc secondary battery in whichthe separator for a zinc secondary battery of the disclosure may beemployed may be, more specifically, a nickel-zinc secondary battery,silver oxide-zinc secondary battery manganese oxide-zinc secondarybattery or zinc-air secondary battery, or another type of alkali zincsecondary battery. The zinc secondary battery may be a battery thatincludes the following reaction at the negative electrode side, forexample.

Zn+40H⁻Zn(OH)₄ ²⁻+2e⁻

Without being limited to any particular principle, it is thought thatthe following may be the principle which allows inhibition of shortcircuiting of the zinc secondary battery by the separator for a zincsecondary battery of the disclosure.

When charge-discharge is repeated in a zinc secondary battery, zincdendrites grow from the negative electrode body and reach beyond theseparator to the positive electrode body, thereby potentially causingshort circuiting of the zinc secondary battery.

One reason for the growth of zinc dendrites is thought to be reductionof Zn(OH)₄ ²⁻ in the electrolyte solution and uneven deposition of theresulting Zn on the negative electrode body. More specifically, forexample, metallic zinc Zn reacts with hydroxide ion OH⁻ at the negativeelectrode by discharge reaction, generating zinc hydroxide (Zn(OH)₂).Zinc hydroxide dissolves in the electrolyte solution, with dissolutionof the zinc hydroxide in the electrolyte solution resulting in diffusionof tetrahydroxozincate ion ([Zn(OH)₄]²⁻) in the electrolyte solution.When tetrahydroxozincate ion is reduced to zinc by charge reaction, thismay promote formation of zinc in a non-homogeneous manner on thenegative electrode. Therefore, inhibiting the supply of Zn(OH)₄ ²⁻ tothe zinc dendrites inhibits growth of the zinc dendrites and therebypresumably inhibits short circuiting of the zinc secondary battery.

Incidentally, Zn(OH)₄ ²⁻ is generally produced during discharge on thenegative electrode body side, but Zn(OH)₄ ²⁻ is also produced on thepositive electrode body side. This is thought to occur because ofirregularities in the concentration of ZnO which dissolves in a fixedamount in the electrolyte solution during charge-discharge of a zincsecondary battery.

The separator for a zinc secondary battery of the disclosure has atitanium oxide-containing porous layer. The titanium oxide-containingporous layer comprises a titanium oxide represented by Ti_(x)O_(y),wherein 0<x, 0<y, and y<2x.

A titanium oxide of this type has an electroconductive property.Consequently, after zinc dendrites grown from the negative electrodeactive material layer side have reached the titanium oxide-containingporous layer, current flowing through the zinc dendrites tends todiffuse in the in-plane direction of the layer. This tends to result inelectrodeposition of zinc in the in-plane direction of the titaniumoxide-containing porous layer. Growth of zinc dendrites to the positiveelectrode body side is therefore inhibited.

Such titanium oxides are also negatively electrified in stronglyalkaline electrolytes. Consequently, Zn(OH)₄ ²⁻ in the electrolyte, andespecially Zn(OH)₄ ²⁻ present on the positive electrode body side, isunlikely to approach the titanium oxide-containing porous layer due toelectrostatic repulsion. This inhibits growth of zinc dendrites throughthe separator toward the positive electrode body side.

FIG. 1 is a separator for a zinc secondary battery 10 according to afirst embodiment of the disclosure.

As shown in FIG. 1, the separator for a zinc secondary battery 10according to the first embodiment of the disclosure has a poroussubstrate layer 12, and a titanium oxide-containing porous layer 11laminated on the porous substrate layer 12.

FIG. 1, however, is not intended to limit the scope of the separator fora zinc secondary battery of the disclosure.

The separator for a zinc secondary battery of the disclosure has aconstruction in which a porous substrate layer, a titaniumoxide-containing porous layer, and a porous substrate layer arelaminated in that order.

If the separator for a zinc secondary battery of the disclosure has sucha construction it will be possible to inhibit sliding of the titaniumoxide down from the titanium oxide-containing porous layer. This canimprove the durability of the titanium oxide-containing porous layer. Itcan therefore also inhibit short circuiting of the zinc secondarybattery. By disposing a porous substrate layer between the titaniumoxide-containing porous layer and the positive electrode body it ispossible to inhibit direct contact between the titanium oxide-containingporous layer and the positive electrode body.

FIG. 2 shows a separator for a zinc secondary battery 10′ according to asecond embodiment of the disclosure.

As seen in FIG. 2, the separator for a zinc secondary battery 10′according to the second embodiment of the disclosure has a poroussubstrate layer 13, a titanium oxide-containing porous layer 11, and aporous substrate layer 12, laminated in that order.

FIG. 2, however, is not intended to limit the scope of the separator fora zinc secondary battery of the disclosure.

The separator for a zinc secondary battery of the disclosure may alsohave a construction in which a nonwoven fabric layer, a porous substratelayer, a titanium oxide-containing porous layer and a porous substratelayer are laminated in that order.

If the separator for a zinc secondary battery of the disclosure has sucha construction it will be possible to situate a nonwoven fabric layerbetween the negative electrode body and the porous substrate layer ofthe separator for a zinc secondary battery of the disclosure when thezinc secondary battery is constructed. This will help hold theelectrolyte solution between the negative electrode body and the poroussubstrate layer. A separator for a zinc secondary battery of thedisclosure having such a construction also can have increased distancebetween the negative electrode body surface on which zinc dendritesform, and the separator for a zinc secondary battery of the disclosure.This will reduce the surface areas of the tips of the zinc dendritesthat have extended from the negative electrode body to the side of theseparator for a zinc secondary battery of the disclosure. This reducesZn(OH)₄ ²⁻ supplied to the tips of zinc dendrites that have extended tothe side of the separator for a zinc secondary battery of thedisclosure. Extension of zinc dendrites is thus further inhibited.

FIG. 3 is a separator for a zinc secondary battery 10″ according to athird embodiment of the disclosure.

As shown in FIG. 3, the separator for a zinc secondary battery 10″according to the third embodiment of the disclosure has a nonwovenfabric layer 14, a porous substrate layer 13, a titaniumoxide-containing porous layer 11, and a porous substrate layer 12,laminated in that order.

FIG. 3, however, is not intended to limit the scope of the separator fora zinc secondary battery of the disclosure.

<Titanium Oxide-Containing Porous Layer>

The titanium oxide-containing porous layer is a porous layer comprisinga titanium oxide. The titanium oxide may be present as particles in thetitanium oxide porous layer.

The “porous” modifier in “titanium oxide porous layer” means that it hasnumerous through-holes running from the front to the back of the layer.

The thickness of the titanium oxide-containing porous layer may be 10 μmto 1000 μm, for example. The thickness of the titanium oxide-containingporous layer may be 10 μm or greater, 50 μm or greater or 100 μm orgreater, and 1000 μm or smaller, 500 μm or smaller or 200 μm or smaller.

The porosity and mean pore size required for the titaniumoxide-containing porous layer may be those commonly required for aseparator for a zinc secondary battery.

The titanium oxide-containing porous layer can be formed by applying anddrying a slurry of titanium oxide particles dispersed in a dispersingmedium, on a porous layer such as the porous substrate layer describedbelow. The method of applying the slurry onto the porous layer is notparticularly restricted, and it may be a publicly known method such asscreen printing, dipping or coating, and more specifically doctor bladecoating, for example. The titanium oxide-containing porous layer mayalso be partially or fully integrated with the porous substrate layer.

The slurry may also comprise a binder such as styrene-butadiene-rubber(SBR) or a thickener such as carboxymethyl cellulose (CMC), in additionto the titanium oxide.

(Titanium Oxide)

The titanium oxide in the titanium oxide-containing porous layer isrepresented by Ti_(x)O_(y), where 0<x, 0<y, and y<2x.

The valency of titanium in this type of titanium oxide is greater than0.00 and less than 4.00. Such titanium oxides also haveelectroconductivity and are negatively electrified in electrolytesolutions.

The valency of titanium in the titanium oxide may be greater than 0.00,0.50 or greater, 1.00 or greater, 2.00 or greater or 3.00 or greater,and less than 4.00, 3.80 or lower, 3.70 or lower, 3.60 or lower or 3.50or lower.

Examples of titanium oxides in the titanium oxide-containing porouslayer include TiO, Ti₂O, Ti₂O₃, Ti₃O, Ti₃O₅, Ti₄O₅, Ti₄O₇, Ti₅O₉, Ti₆O,Ti₆O₁₁, Ti₇O₁₃, Ti₈O₁₅ and Ti₉O₁₇, as well as their combinations, withno limitation to these.

When the titanium oxide-containing porous layer comprises titanium oxideparticles, the mean primary particle size of the titanium oxideparticles may be 10 nm to 1000 μm.

The mean primary particle size of the titanium oxide particles may be 10nm or greater, 100 nm or greater, 10 μm or greater or 50 μm or greater,and 1000 μm or smaller, 500 μm or smaller, 250 μm or smaller or 100 μmor smaller.

The mean primary particle size of the titanium oxide particles can bedetermined as the circle equivalent diameter by observation with ascanning electron microscope (SEM). A large number of samples ispreferred, the number being 20 or greater, 50 or greater or 100 orgreater, for example.

The mean primary particle size of the titanium oxide particles can beappropriately determined by a person skilled in the art, according tothe porosity and pore size required for the titanium oxide-containingporous layer. A larger mean primary particle size for the titanium oxideparticles increases the porosity and pore size of the titaniumoxide-containing porous layer, while a smaller mean primary particlesize of the titanium oxide particles tends to lower the porosity andpore size of the titanium oxide-containing porous layer.

<Porous Substrate Layer>

The porous substrate layer is a porous layer having an insulatingproperty and having through-holes running through both sides of thefilm. The porous substrate layer may be hydrophobic or hydrophilic.

The porosity rate and pore size of the porous substrate layer may be aporosity and pore size generally required for a separator for a zincsecondary battery.

The thickness of the porous substrate layer may be 10 μm to 1000 μm, forexample. The thickness of the conductive porous substrate layer may be10 μm or greater, 50 μm or greater or 100 μm or greater, and 1000 μm orsmaller, 500 μm or smaller or 200 μm or smaller.

The porous substrate layer used may be a resin porous layer, and morespecifically a polyolefin-based porous layer, polyamide-based porouslayer or nylon-based porous layer, with no limitation to these.

The porous resin film may be hydrophilicized by adding a hydrophilicfunctional group, for example.

The “porous” modifier in “porous substrate layer” means that it hasnumerous through-holes running from the front to the back of the layer.The porous substrate layer may therefore be a sponge layer, for example.

<Nonwoven Fabric Layer>

The nonwoven fabric layer may be any nonwoven fabric layer that can beused as a constituent element of a separator layer in a zinc secondarybattery. Examples of such nonwoven fabrics include cellulose-basednonwoven fabrics.

<Zinc Secondary Battery>

The zinc secondary battery of the disclosure has a separator for a zincsecondary battery of the disclosure.

The zinc secondary battery of the disclosure may have a publicly knownconstruction, except for using a separator for a zinc secondary batteryof the disclosure as the separator.

The zinc secondary battery of the disclosure may be a zinc secondarybattery having a negative electrode body, a separator for a zincsecondary battery and a positive electrode body in that order, forexample, with the negative electrode body, the separator for a zincsecondary battery and the positive electrode body being impregnated withan electrolyte solution.

Typically, the zinc secondary battery of the disclosure will be a zincsecondary battery having a negative electrode body, a separator and apositive electrode body housed in that order in a battery case, andhaving the battery case filled with an electrolyte solution. Morespecifically, the zinc secondary battery of the disclosure may be anickel-zinc secondary battery, silver oxide-zinc secondary batterymanganese oxide-zinc secondary battery, zinc-air secondary battery, oranother type of alkali zinc secondary battery.

FIG. 4 is a zinc secondary battery 100 according to a first embodimentof the disclosure.

As shown in FIG. 4, the zinc secondary battery 100 according to thefirst embodiment of the disclosure has a negative electrode body 20, aseparator for a zinc secondary battery 10″ according to the thirdembodiment of the disclosure, and a positive electrode body 30,laminated in that order. These are housed in a battery case 50 filledwith an electrolyte solution 40.

Incidentally, the negative electrode body 20 has a construction in whicha negative electrode active material layer 22 is formed on a negativeelectrode collector 21. The positive electrode body 30 has aconstruction in which a positive electrode active material layer 32 isformed on a positive electrode collector 31.

<Negative Electrode Body>

The negative electrode body may be one in which the surface of thenegative electrode collector is covered by a zinc-based negativeelectrode active material layer.

The negative electrode collector may be a conductive material, forexample, a metal such as stainless steel, aluminum, copper, nickel, ironor titanium, or carbon, with no limitation to these. The material of thenegative electrode collector may be copper.

The form of the current collector layer is not particularly restrictedand may be, for example, rod-shaped, foil-shaped, plate-shaped,mesh-like or porous. The collector may be metal Celmet.

The zinc-based negative electrode active material layer comprises zincand zinc oxide, and an optional binder and other additives. Thezinc-based negative electrode active material layer may further comprisea zinc compound such as calcium zincate, for example.

Examples of binders include, but are not limited to,styrene-butadiene-rubber (SBR).

<Separator for Zinc Secondary Battery>

The zinc secondary battery of the disclosure has a separator for a zincsecondary battery of the disclosure.

<Positive Electrode Body>

The positive electrode body may be one in which the surface of thepositive electrode collector is covered by a positive electrode activematerial layer.

The description for the positive electrode collector is the same as forthe negative electrode collector, substituting “positive electrodecollector” for “negative electrode collector”. The material of thepositive electrode collector may be aluminum. If the material of thepositive electrode collector is nickel, then the positive electrodecollector may be nickel Celmet.

The positive electrode active material layer comprises a positiveelectrode active material, and optionally a binder and other additives.The positive electrode active material may be appropriately selecteddepending on the type of zinc secondary battery. When the zinc secondarybattery is a nickel zinc secondary battery, for example, the positiveelectrode active material may comprise nickel hydroxide and/or nickeloxyhydroxide.

For the binder, refer to the description of the negative electrode body.

<Electrolyte Solution>

The electrolyte solution may be an aqueous solution, and morespecifically an alkali electrolyte solution. The alkali electrolytesolution may be an electrolyte solution comprising an alkali metalhydroxide, and more specifically potassium hydroxide, sodium hydroxide,lithium hydroxide or ammonium hydroxide. The electrolyte solution ispreferably potassium hydroxide. Other inorganic or organic additives mayalso be present in the electrolyte solution.

Zinc oxide may also be dissolved in the electrolyte solution. The zincoxide may be dissolved in the electrolyte solution in a state ofsaturation at ordinary temperature.

EXAMPLES Example 1

A separator for a zinc secondary battery was prepared for Example 1 inthe following manner.

(Preparation of Ink)

TiO powder as titanium oxide particles, styrene-butadiene-rubber (SBR)and carboxymethyl cellulose (CMC) were weighed out to a mass ratio ofTiO powder:SBR:CMC=97:2.5:0.5 in the titanium oxide-containing porouslayer to be formed, and a total of 2 g.

The TiO powder and CMC were placed in a mortar and kneaded. The kneadedmaterial was then placed in a container and stirred at 2000 rpm for 1minute with an Awatori Rentaro (product of Thinky Corp.). SBR was thenadded to the kneaded material, and the mixture was stirred at 2000 rpmfor 3 minutes with an Awatori Rentaro (product of Thinky Corp.) toprepare an ink.

(Formation of Intermediate Layer)

A polypropylene (PP) separator as the porous substrate layer wasattached onto a glass panel with masking tape, while being pulled withapplication of slight tensile force from both ends in the longitudinaldirection. The PP separator was subjected to prior hydrophilicizingtreatment.

The ink was coated onto the surface of the PP separator by doctor bladecoating. The blade gap was 125 μm. The coated ink was then allowed tonaturally dry, and then further dried at 40° C. for 10 hours with avacuum drier. This formed a TiO-containing porous layer as anintermediate layer on the PP separator.

(Separator Assembly)

A separate hydrophilicized PP separator was disposed on theTiO-containing porous layer, and then a hydrophilicized cellulose-basednonwoven fabric separator was disposed over this to prepare a separatorfor Example 1.

The separator of Example 1 had a construction with the cellulose-basednonwoven fabric separator, PP separator, TiO-containing porous layer andPP separator stacked in that order.

Example 2

A separator for Example 2 was prepared in the same manner as Example 1,except that Ti₂O₃ powder was used instead of TiO powder.

The separator of Example 2 had a construction with the cellulose-basednonwoven fabric separator, PP separator, Ti₂O₃-containing porous layerand PP separator stacked in that order.

Comparative Example 1

A separator for Comparative Example 1 was prepared in the same manner asExample 1, except that an intermediate layer was not formed on the PPseparator.

The separator of Comparative Example 1 had a construction with thecellulose-based nonwoven fabric separator, PP separator and PP separatorstacked in that order.

Comparative Example 2

A separator for Comparative Example 2 was prepared in the same manner asExample 1, except that Ti powder was used instead of TiO powder.

The separator of Comparative Example 2 had a construction with thecellulose-based nonwoven fabric separator, PP separator, Ti-containingporous layer and PP separator stacked in that order.

Comparative Example 3

A separator for Comparative Example 3 was prepared in the same manner asExample 1, except that TiO₂ powder was used instead of TiO powder.

The separator of Comparative Example 3 had a construction with thecellulose-based nonwoven fabric separator, PP separator, TiO₂-containingporous layer and PP separator stacked in that order.

Comparative Example 4

A separator for Comparative Example 4 was prepared in the same manner asExample 1, except that Cu—Sn alloy powder was used instead of TiOpowder.

The separator of Comparative Example 4 had a construction with thecellulose-based nonwoven fabric separator, PP separator, Cu—Snalloy-containing porous layer and PP separator stacked in that order.

Comparative Example 5

A separator for Comparative Example 5 was prepared in the same manner asExample 1, except that TiN powder was used instead of TiO powder.

The separator of Comparative Example 5 had a construction with thecellulose-based nonwoven fabric separator, PP separator, TiN-containingporous layer and PP separator stacked in that order.

Comparative Example 6

A separator for Comparative Example 6 was prepared in the same manner asExample 1, except that TiB₂ powder was used instead of TiO powder.

The separator of Comparative Example 6 had a construction with thecellulose-based nonwoven fabric separator, PP separator, TiB₂-containingporous layer and PP separator stacked in that order.

Comparative Example 7

A separator for Comparative Example 7 was prepared in the same manner asExample 1, except that ZrC powder was used instead of TiO powder.

The separator of Comparative Example 7 had a construction with thecellulose-based nonwoven fabric separator, PP separator, ZrC-containingporous layer and PP separator stacked in that order.

Comparative Example 8

A separator for Comparative Example 8 was prepared in the same manner asExample 1, except that TiC powder was used instead of TiO powder.

The separator of Comparative Example 8 had a construction with thecellulose-based nonwoven fabric separator, PP separator, TiC-containingporous layer and PP separator stacked in that order.

<Fabrication of Zinc Secondary Battery>

Nickel zinc secondary batteries employing different separators werefabricated in the following manner.

(Positive Electrode Body)

Ni(OH)₂, SBR and CMC were each weighed out to a mass ratio ofNi(OH)₂:SBR:CMC=97:2.5:0.5. The Ni(OH)₂ included an auxiliary agent.

The materials were kneaded with a mortar, water was added to adjust thehardness, and the mixture was stirred for 1 minute at 2000 rpm using anAwatori Rentaro (product of Thinky Corp.) to prepare a positiveelectrode active material slurry.

The positive electrode active material slurry was coated by doctor bladecoating onto the surface of a nickel foil as a positive electrodecollector. The coated positive electrode active material slurry was thenallowed to naturally dry, and further dried at 80° C. overnight in areduced pressure environment. A positive electrode body was thus formed.

(Negative Electrode Body)

ZnO, Zn, SBR and CMC were each weighed out to a mass ratio ofZnO:Zn:SBR:CMC=76:21:2.5:0.5.

The materials were kneaded with a mortar, water was added to adjust thehardness, and the mixture was stirred for 1 minute at 2000 rpm using anAwatori Rentaro (product of Thinky Corp.) to prepare a negativeelectrode active material slurry.

The negative electrode active material slurry was coated by doctor bladecoating onto the surface of a copper foil as a negative electrodecollector. The coated negative electrode active material slurry was thenallowed to naturally dry, and further dried at 80° C. overnight in areduced pressure environment. A negative electrode body was thus formed.

(Assembly of Zinc Secondary Battery)

The positive electrode body, separator and negative electrode body werelaminated in that order and housed in a battery case. The battery casewas then filled with an electrolyte solution to obtain a zinc secondarybattery. The separator was disposed with the nonwoven fabric layerfacing the negative electrode body side. The electrolyte solution was a6 mol/L KOH aqueous solution with ZnO dissolved in a state of saturationat 25° C.

<Cycle Stability Evaluation>

A cycle test was carried out for each of the nickel zinc secondarybatteries employing different examples of separators, and the number ofcycles to short circuiting was measured.

The cycle test was conducted using an electrochemical measurement system(VMP3, product of Bio-Logic) and a thermostatic bath (SU-642, product ofEspec Corp.). The temperature of each nickel zinc secondary batteryduring the measurement was 25° C.

The cycle test was carried out with a charge-discharge range of 0% to50% state of charge (SOC), with the theoretical charge capacity of thepositive electrode active material layer as 100%. The C rate was 3.5mA/cm². The cut voltage was 2 V during charge and 1.3 V duringdischarge. The cycle test was carried out with an interval of 5 minutesbetween each cycle.

<Results>

The construction of the separator and the cycle stability evaluationresults for each example are shown in Table 1. FIG. 5 is a graph showingevaluation results for cycle stability in Comparative Examples 2 and 3and Examples 1 and 2. In Table 1, the cycle stability evaluation resultsare listed with the number of cycles to short circuiting in ComparativeExample 1 as 100%. The valency of Ti is only listed for ComparativeExamples 2 and 3 and Examples 1 and 2. In FIG. 5, the ordinate shows theratio of the durability in each example with respect to the durabilityin Comparative Example 1, and the abscissa shows the valency oftitanium.

TABLE 1 Construction Porous Result substrate Intermediate Poroussubstrate Nonwoven fabric Titanium Durability Example layer layer layerlayer valency (%) Comp. Ex. 1 PP porous None PP porous layer Cellulosenonwoven — 100 layer fabric layer Comp. Ex. 2 PP porous Ti-containing PPporous layer Cellulose nonwoven 0 121 layer porous layer fabric layerExample 1 PP porous TiO-containing PP porous layer Cellulose nonwoven 2171 layer porous layer fabric layer Example 2 PP porous Ti₂O₃- PP porouslayer Cellulose nonwoven 3 168 layer containing fabric layer porouslayer Comp. Ex. 3 PP porous TiO₂-containing PP porous layer Cellulosenonwoven 4 116 layer porous layer fabric layer Comp. Ex. 4 PP porousCu—Sn alloy- PP porous layer Cellulose nonwoven — 96 layer containingfabric layer porous layer Comp. Ex. 5 PP porous TiN-containing PP porouslayer Cellulose nonwoven — 57 layer porous layer fabric layer Comp. Ex.6 PP porous TiB₂-containing PP porous layer Cellulose nonwoven — 24layer porous layer fabric layer Comp. Ex. 7 PP porous ZrC-containing PPporous layer Cellulose nonwoven — 64 layer porous layer fabric layerComp. Ex. 8 PP porous TiC-containing PP porous layer Cellulose nonwoven— 45 layer porous layer fabric layer

As shown in Table 1 and FIG. 5, the durability was 171% in Example 1which employed a TiO-containing porous layer as the intermediate layer,which was significantly higher durability compared to ComparativeExample 1 which did not have an intermediate layer. The durability was168% even in Example 2 which employed a Ti₂O₃-containing porous layer asthe intermediate layer, which was likewise significantly higherdurability compared to Comparative Example 1 which did not have anintermediate layer.

In contrast, in Comparative Example 2 which employed a Ti-containingporous layer and Comparative Example 3 which employed a TiO₂-containingporous layer as the intermediate layer, the durability values were 121%and 116%, respectively, which was slightly higher durability compared toComparative Example 1 which did not have an intermediate layer. However,the degree of increase in durability in Comparative Examples 2 and 3 wasless than in Examples 1 and 2.

In Comparative Examples 4 to 8 which employed porous layers containingmetals other than titanium or titanium oxides, the durability valueswere 96%, 57%, 24%, 64% and 45%, in that order, and therefore all hadlower durability than Comparative Example 1 which did not have anintermediate layer.

REFERENCE SIGNS LIST

-   10, 10′, 10″ Separator-   11 Titanium oxide-containing porous layer-   12, 13 Porous substrate layer-   14 Nonwoven fabric layer-   20 Negative electrode body-   21 Negative electrode collector-   22 Negative electrode active material layer-   30 Positive electrode body-   31 Positive electrode collector-   32 Positive electrode active material layer-   40 Electrolyte solution-   50 Battery case-   100 Zinc secondary battery

1. A separator for a zinc secondary battery, having a porous substratelayer and a titanium oxide-containing porous layer laminated onto theporous substrate layer, wherein the titanium oxide-containing porouslayer comprises a titanium oxide represented by Ti_(x)O_(y), where 0<x,0<y, and y<2x.
 2. The separator for a zinc secondary battery accordingto claim 1, wherein the titanium oxide is TiO, Ti₂O, Ti₂O₃, Ti₃O, Ti₃O₅,Ti₄O₅, Ti₄O₇, Ti₅O₉, Ti₆O, Ti₆O₁₁, Ti₇O₁₃, Ti₈O₁₅ or Ti₉O₁₇.
 3. Theseparator for a zinc secondary battery according to claim 1, wherein theporous substrate layer, the titanium oxide-containing porous layer andthe porous substrate layer are laminated in that order.
 4. The separatorfor a zinc secondary battery according to claim 3, wherein a nonwovenfabric layer, the porous substrate layer, the titanium oxide-containingporous layer and the porous substrate layer are laminated in that order.5. The separator for a zinc secondary battery according to claim 1,wherein the porous substrate layer is a resin porous layer.
 6. Theseparator for a zinc secondary battery according to claim 5, wherein theresin porous layer is a polyolefin-based porous layer, a polyamide-basedporous layer or a nylon-based porous layer.
 7. A zinc secondary batteryhaving a separator for a zinc secondary battery according to claim
 1. 8.The zinc secondary battery according to claim 7, which has a negativeelectrode body, the separator for a zinc secondary battery and apositive electrode body in that order, and the negative electrode body,the separator for a zinc secondary battery and the positive electrodebody are impregnated with an electrolyte solution.
 9. The zinc secondarybattery according to claim 8, wherein the electrolyte solution is anaqueous solution.
 10. The zinc secondary battery according to claim 8,wherein the electrolyte solution is an alkali electrolyte solution. 11.The zinc secondary battery according to claim 8, wherein zinc oxide isdissolved in the electrolyte solution.